1. Field of Invention
The present invention relates to a power supply circuit of an electro-optical device, a driving circuit of an electro-optical device, a method of driving an electro-optical device, an electro-optical device, and an electronic equipment, in which a reduced number of components are mounted.
2. Description of Related Art
In general, electro-optical devices can be classified into various types according to the driving method or the electrode structure. In an electro-optical device of the simplest type, a plurality of scanning electrodes (scanning lines) are formed on one substrate, a plurality of data electrodes (data lines) are formed on the other substrate, and an electro-optical material such as a liquid crystal is disposed between these two substrates, whereby an image is displayed by means of an electro-optical change caused by a potential difference between the two electrodes.
In such an electro-optical device, a selection voltage required to drive the electro-optical material is generally in the range of 20 to 25 V, which is much higher than input voltages of 3 to 5 V applied to logic circuits. In order to obtain such a high selection voltage, electro-optical devices generally include a power supply circuit using a charge pump circuit which generates the selection voltage by stepping up a voltage supplied from a single power supply.
However, the technique of generating the selection voltage using the charge pump circuit needs as many capacitors as the voltage stepping-up factor. In electro-optical devices, as described above, the input voltage has to be stepped up by a large factor to obtain the selection voltage, and thus the charge pump circuit needs a large number of capacitors.
Capacitors used in power supply circuits are generally large in size, and thus it is difficult to form them on semiconductor substrates. In most cases, therefore, capacitors of power supply circuits are not integrated on semiconductor chips, but they are instead mounted as external components. Therefore, if a large number of capacitors are used, the result is an increase in the total cost and an increase in complexity of the assembly process which causes a reduction in the production efficiency.
In view of the above problems, it is an object of the present invention to provide a power supply circuit of an electro-optical device, a driving circuit of an electro-optical device, a method of driving an electro-optical device, an electro-optical devices and an electronic equipment using an electro-optical device, which need a less number of externally mounted components and thus which allows simplification of the assembly process and a reduction in cost.
According to a first aspect of the present invention, to achieve the above object, there is provided a power supply circuit for supplying a potential to an electro-optical device which includes a plurality of scanning lines and a plurality of data lines, the scanning lines crossing the data lines, and the potential serving as a selection voltage for selecting a scanning line. The power supply circuit may consist of a voltage generation circuit for generating one of a selection voltage having a positive polarity and a selection voltage having a negative polarity, defined with respect to a median value of signal voltages applied to the data lines; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a switching element; and an inductor that stores electric power between a first input voltage and a second input voltage when the switching element turns on, and that releases the stored electric power when the switching element turns off, whereby, using the electric power released from the inductor, the voltage generation circuit generates the one of selection voltage having a positive polarity and the selection voltage having a negative polarity with respect to the median value of signal voltages applied to the data lines.
In the power supply circuit according to the first aspect, either one of the selection voltages having positive and negative polarities applied to the scanning lines is generated by the voltage generation circuit using electric power which is released from the inductor when the switching element is turned off. This allows the one selection voltage to become greater than the difference between the first and second input potentials. Furthermore, in the power supply circuit according to the first aspect, the other selection voltage is generated by the inverter circuit by inverting the polarity of the one selection voltage stored in the voltage storage element after being generated by the voltage generation circuit. Thus, in the power supply circuit according to the first aspect of the present invention, it is possible to reduce the number of components such as voltage storage elements which cannot be formed on a semiconductor substrate, and thus, which have to be externally mounted without causing an increase in electric power consumption. Therefore, the first aspect of the present invention allows the components to be mounted in a simpler fashion, and brings about cost reduction. As for the voltage storage element used in the present invention, a capacitor or a secondary battery capable of charging and discharging may be employed. The capacitor is more desirable because it can be produced in a small form.
In the power supply circuit according to the first aspect, the voltage generation circuit preferably further includes a control circuit for controlling a turning-on/off operation of the switching element in accordance with a comparison result of a voltage based on the electric power released from the inductor with respect to a target voltage. In this circuit configuration, the turning-on/off of the switching element is controlled by feeding back the output voltage, thereby regulating the selection voltage having the inverted polarity as well as the selection voltage having the non-inverted polarity, regardless of the load.
Preferably, the switching element is turned on and off using a pulse signal such that the generated electric power is controlled by adjusting the pulse width or the pulse intervals.
According to a second aspect, to achieve the above-described object, there is provided a power supply circuit for supplying a voltage to an electro-optical device including a plurality of scanning lines and a plurality of data lines, the scanning lines crossing the data lines, and the potential serving as a selection voltage for selecting a scanning line from the plurality of scanning lines. The power supply circuit may consist of a voltage generation circuit for generating one of a selection voltage having a positive polarity and a selection voltage having a negative polarity, defined with respect to a median value of signal voltages applied to the data lines; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a transformer which inputs a pulse signal via a primary side of the transformer, the voltage generation circuit generating the one of the selection voltage having a positive polarity and the selection voltage having a negative polarity using a voltage output from a secondary side of the transformer.
In the power supply circuit according to the second aspect, either one of the selection voltages having positive and negative polarities applied to the scanning lines is generated by the voltage generation circuit using a voltage obtained by stepping up a signal via the transformer. In this technique, the one selection voltage having a high voltage can be easily generated. Furthermore, as compared with the first aspect of the present invention, the switching element can be turned on and off with less electric power consumption, which results in a reduction in the total power consumption. Furthermore, in the power supply circuit according to the second aspect of the present invention, the other selection voltage is generated using the inverter circuit by inverting the polarity of the one selection voltage stored in the voltage storage element after being generated by the voltage generation circuit. Thus, as in the power supply circuit according to the first aspect of the present invention, it is possible to reduce the number of components such as a voltage storage element which cannot be formed on a semiconductor substrate, and thus, which have to be externally mounted. Thus, also in this second aspect of the invention, simplification of the assembly process and a reduction in cost can be achieved.
In this second aspect of the present invention, the transformer is preferably a piezoelectric transformer which generates mechanical vibration in response to a voltage applied to the primary side of the transformer, which converts the mechanical vibration to a voltage, and which outputs the voltage resulting, from the secondary side. The use of the piezoelectric transformer allows a reduction in size. Furthermore, if the resonance frequency of mechanical vibration is set to a value close to the natural frequency, an increase in the voltage conversion efficiency can be achieved.
In the power supply circuit according to the present invention, the voltage generation circuit preferably further includes a control circuit for controlling a supply of the pulse signal to the primary side of the transformer in accordance with a comparison result of a voltage based on an output from the secondary side of the transformer with respect to a target voltage. In this circuit configuration, the pulse signal is controlled by feeding back the output voltage, thereby regulating the selection voltage having the inverted polarity, as well as the original selection voltage having the non-inverted polarity, regardless of the load. Furthermore, it is possible to control the generated electric power by adjusting the pulse width or the pulse intervals.
In the power supply circuit according to the first or second aspect of the present invention, the inverter circuit preferably includes a voltage storage element having an electrode connected to a voltage terminal which is switched in response to a clock signal so that the voltage is stored and released in a highly efficient manner.
In the first or second aspect of the present invention, when only a first area covered by some of the plurality of scanning lines is displayed and a second area covered by the remaining scanning lines is not displayed, and when a scanning line in the second area is selected, it is desirable that the polarity inversion by the inverter circuit be disabled or be performed at a reduced frequency. In this technique, when a scanning line which is not involved in displaying an image is selected, the inverting operation of the inverter circuit is disabled or is performed at a reduced frequency thereby preventing useless power consumption.
According to an another aspect of the present invention, to achieve the above object, there is provided a driving circuit of an electro-optical device, for driving pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The driving circuit may consist of a power supply circuit for generating a selection voltage having a positive polarity and a selection voltage having a negative polarity, the positive polarity and the negative polarity being defined with respect to a median value of signal voltages applied to the data lines; and a scanning line driving circuit for applying the selection voltage having a positive polarity and the selection voltage having a negative polarity, generated by the power supply circuit, to respective scanning lines in a predetermined order. The power supply circuit may consist of a voltage generation circuit for generating one of the selection voltage having a positive polarity and the selection voltage having a negative polarity, from a first input potential and a second input potential; a voltage storage element for storing a voltage based on the selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a switching element; and an inductor which stores electric power between the first input potential and the second input potential when the switching element turns on, and which releases the stored electric power when the switching element turns off whereby the voltage generation circuit generates the one of the selection voltage having a positive polarity and the selection voltage having a negative polarity using the electric power released from the inductor. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the first aspect, and thus, it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved.
According to still another aspect of the present invention, there is provided a driving circuit of an electro-optical device, for driving pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The driving circuit may consist of a power supply circuit for generating a selection voltage having a positive polarity and a selection voltage having a negative polarity, the positive polarity and the negative polarity being defined with respect to a median value of signal voltages applied to the data lines; and a scanning line driving circuit for applying the selection voltage having a positive polarity and the selection voltage having a negative polarity, generated by the power supply circuit, to the respective scanning lines in a predetermined order. The power supply circuit may consist of a voltage generation circuit for generating one of the selection voltage having a positive polarity and the selection voltage having a negative polarity, from a first input potential and a second input potential; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit including a transformer which receives a pulse signal via a primary side of the transformer, and the voltage generation circuit generating the one of the selection voltage having a positive polarity and the selection voltage having a negative polarity using a voltage output from a secondary side of the transformer. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the second aspect, and thus it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved.
According to still another aspect of the present invention, to achieve the above object, there is provided a method of driving an electro-optical device, for driving pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The method may consist of a first step of turning on and turning off a switching element such that, when the switching element is turned on, electric power is stored in an inductor between a first input potential and a second input potential, and when the switching element is turned off, the electric power stored in the inductor is released, thereby generating one of a selection voltage having a positive polarity and a selection voltage having a negative polarity with respect to a median value of signal voltages supplied to the data lines, and storing a voltage based on the one of selection voltage; and a second step of inverting the polarity of the voltage stored in the first step, with respect to a predetermined value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity, selection voltages generated in the first step and the second step being applied to respective scanning lines in a predetermined order. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the first aspect, and thus, it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved.
According to still another aspect of the present invention, there is provided a method of driving an electro-optical device, for driving pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The method may consist of a first step of inputting a pulse signal to a primary side of a transformer, and generating, using a voltage output from a secondary side of the transformer, one of a selection voltage having a positive polarity and a selection voltage having a negative polarity with respect to a median value of signal voltages supplied to the data lines, and storing a voltage based on the one selection voltage; and a second step of inverting the polarity of the voltage stored in the first step, with respect to a predetermined value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity, selection voltages generated in the first step and the second step being applied to respective scanning lines in a predetermined order. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the second aspect, and thus it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved.
According to still another aspect of the present invention, to achieve the above object, there is provided an electro-optical device which may consist of pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The electro-optical device may further consist of a power supply circuit for generating a selection voltage having a positive polarity and a selection voltage having a negative polarity, the positive polarity and the negative polarity being defined with respect to a median value of signal voltages applied to the data lines; and a scanning line driving circuit for applying the selection voltage having a positive polarity and the selection voltage having a negative polarity, generated by the power supply circuit, to respective scanning lines in a predetermined order. The power supply circuit may consist of a voltage generation circuit for generating one of the selection voltage having a positive polarity and the selection voltage having a negative polarity, from a first input potential and a second input potential; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a switching element; and an inductor which stores electric power between the first input potential and the second input potential when the switching element turns on, and which releases the stored electric power when the switching element turns off, whereby the voltage generation circuit generates the one of the selection voltage having a positive polarity and the selection voltage having a negative polarity using the electric power released from the inductor. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the first aspect, and thus, it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved.
According to still another aspect of the present invention, to achieve the above object, there is provided an electro-optical device which may consist of pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The electro-optical device may further consist of a power supply circuit for generating a selection voltage having a positive polarity and a selection voltage having a negative polarity, the positive polarity and the negative polarity being defined with respect to a median value of signal voltages supplied to the data lines; and a scanning line driving circuit for applying the selection voltage having a positive polarity and the selection voltage having a negative polarity, generated by the power supply circuit, to respective scanning lines in a predetermined order. The power supply circuit may consist of a voltage generation circuit for generating one of the selection voltage having a positive polarity and the selection voltage having a negative polarity, from a first input potential and a second input potential; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. The voltage generation circuit may consist of a transformer which inputs a pulse signal via a primary side of the transformer, and the voltage generation circuit generates the one of the selection voltage having positive polarity and the selection voltage having a negative polarity using a voltage output from the secondary side of the transformer. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the second aspect, and thus it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved.
According to still another aspect of the present invention, there is provided an electro-optical device which may consist of pixels disposed at intersections between a plurality of scanning lines and a plurality of data lines. The electro-optical device may further consist of a power supply circuit for generating a selection voltage having a positive polarity and a selection voltage having a negative polarity, the positive polarity and the negative polarity being defined with respect to a median value of signal voltages applied to the data lines. The power supply circuit may consist of a voltage generation circuit for generating one of the selection voltage having a positive polarity and the selection voltage having a negative polarity from a first input potential and a second input potential using an inductor or a transformer driven in response to a pulse signal; a voltage storage element for storing a voltage based on the one selection voltage generated by the voltage generation circuit; and an inverter circuit for inverting the polarity of the voltage stored in the voltage storage element with respect to a predetermined reference value, and outputting the inverted voltage as another one of the selection voltage having a positive polarity and the selection voltage having a negative polarity. When only a first area covered by some of the plurality of scanning lines is displayed and a second area covered by remaining scanning lines is not displayed, and when a scanning line in the second area is selected, polarity inversion by the inverter circuit is not performed or is performed at a reduced frequency. The configuration according to the present aspect also allows a reduction in the number of components such as a voltage storage element, as in the previous aspects, and thus it becomes possible to install the components in a simpler fashion, and a reduction in cost can be achieved. Furthermore, in this technique, when a scanning line which is not involved in displaying an image is selected, the inverting operation of the inverter circuit is disabled or is performed at a reduced frequency, thereby preventing useless power consumption.
According to still another aspect of the present invention, there is provided an electronic equipment which may consist of the electro-optical device according to one of above aspects as a display unit. This electronic equipment also has the advantage in that a less number of externally mounted components are required, and thus, simplification of the assembly process and a reduction in cost can be achieved.
In the present invention, the inductor or the piezoelectric transformer may be disposed on a substrate of a liquid crystal panel or on a flexible board whose terminals formed on one end are connected to the substrate of the liquid crystal panel, or otherwise on a printed circuit board connected to the other end of the flexible board. In the conventional technique, a great number of capacitors used in the power supply circuit are mounted on the printed circuit board or the like. In contrast, the present invention needs a greatly reduced number of capacitors mounted on the circuit board or the like, which makes it possible to miniaturize the device.